2 tube microphone preamps sharing a tube PSU?

[hereforever]

I have an RCA BA-2C clone (minus the power supply) that I am looking to power from a tube PSU for another preamp
The PSU is a Gates SA-77 module (designed to run 1 or 2 SA-70 or SA-73 preamps).  I currently use the SA-77 to power the SA-70 that I bought it with. 
Both would run off of 250V B+ supply

Is there any reason not to simply wire both preamps to the SA-77 module?  I'd like to avoid modifying any of the circuitry but if its advisable to add another stage of power filtering I would consider it

Here's some info about the Gates power supply-
https://www.americanradiohistory.com/Archive-Catalogs/Gates-Harris/Gates-Speech-Input-Equipment-and-Price-List-1950.pdf
(page 29 gives the specs for the SA77 psu)
current ratings- 2A filament & 10ma plate

 

[hereforever]

RCA BA-2C

 

[hereforever]

Gates SA-70

 

[PRR]

Yes.

 

[Winston OBoogie]

Most all of the older valve desks used a common supply for the amps.  The transformer primary of your BA-2 amps which is used to feed DC to the anode will provide some isolation from channel to channel but I think a nominal series resistor shunt capacitor located on each BA-2 channel would be advisable.

Not exactly sure of the particular question  PRR's more succinct reply is answering
The only explicit one I found was:
"Is there any reason not to simply wire both preamps to the SA-77 module?"

Regardless, I would always bow to his wisdom on this stuff. 

 

[emrr]

The PSU is in range for the BA-2, so run them together.  May require DC adjustment through resistor change, I haven't looked at that PSU schematic in awhile. 

 

[Winston OBoogie]

I bow to Doug's wisdom too, he's seen more of this stuff than I've had hot dinners.

 

[hereforever]

Thanks for the responses!

 

[emrr]

3.4mA for SA-70 at 250V.  BA-2 is?  Don't recall.  Maybe 5 mA, not much more. 

The SA-77 says 30mA at 250VDC continuous.  It can power NINE SA-70's no problem, just can't cover more than 2 for filament. 

Important thing with an original BA-2 is not having too much current through the output transformer:  if voltage looks really high then current will be higher too.  288V at the first filter condenser.  232V at the plate of V2.  Mated with the SA-77 you should be somewhat in the same ballpark, if not, then R1 and/or R2 in the SA-77 need to change to compensate.  They will probably need to be larger values to get the BA-2 in range. 

The SA-70 will be fine wherever it lands; no current in any transformers to worry about.  You won't go over on cap voltage either. 

 

[PRR]

> BA-2 is?  Don't recall.  Maybe 5 mA, not much more. 

I cheated, perhaps unwisely. BA-2 has a 220 tap on V2 cathode resistor. I *assume* this is switched to the VU meter for monitoring tube health. Taking 0.7V on 220 I get 3mA in V2. V1 has huge plate resistor and will be <1mA.

2A heater ought to be enough for these tubes.

Yes, trim the drop resistors. For "serious" use we liked plenty of B+ for low THD when driving orchestra through a mile of cable. In today's world of small studios and near-perfect chips, you want "low" B+ to get some "color" without smoking your ADC. 200V may be fine.